A. Tabata

Characterization of lattice-matched and strained GaInAs/AlInAs HEMT structures by photoluminescence spectroscopy

Abstract Low-temperature photoluminescence (PL) measurements have been performed in order to characterize In x Ga 1− x As /In 0.52 Al 0.48 As high electron mobility transistor (HEMT) structures with both lattice-matched ( x In =0.53) and strained ( x In =0.60and 0.65) channels. Samples with electron sheet concentration (n s ) between 0.7 and 3.0 × 10 12 cm -2 have been studied. Strong recombination processes involving the first (E1) and second (E2) electron level with the first heavy-hole level (H1) have been observed. In some cases the parity forbidden transition E2H1 was more intense than the fundamental E1H1 due to its more efficient wave function overlap. Thanks to the Fermi edge enhancement mechanism, we have measured the electron Fermi level (E F ) relatively to the bottom of the n = 2 and n = 1 electron subbands. The values of n s have been deduced from PL measurements and are in good agreement with those measured by transport experiments.

Strain relaxation studied by photoluminescence and by double crystal X-ray diffraction measurements in strained InGaAs

Photoluminescence (PL) and double crystal X-ray diffraction (DCXD) experiments have been carried out on strained View the MathML sourceAs grown on InP substrate by molecular beam epitaxy with different epilayer thicknesses, in order to study lattice relaxation. Samples with tensile strain (View the MathML source) and compressive strain (View the MathML source) have been investigated. Strain was measured by DCXD in conjunction with detailed rocking curve analysis within a dynamical framework. From PL results, we have evaluated the strain values in two different ways. First, we used the PL transition shift induced by strain and second, from PL temperature dependence we measured the heavy-hole-light-hole splitting, which is a direct measurement of strain. Our results have shown good agreement between PL and DCXD measurements and also the existence of residual strain even in samples with a thickness considerably greater than the critical layer thickness.

Temperature dependence of the photoreflectance of strained and lattice-matched InGaAs/InAlAs single quantum wells

Abstract Temperature dependence of photoreflectance spectra is reported for lattice-matched and strained InxGa1−xAs/In0.52Al0.48As (x = 0.53 or 0.60) single quantum wells with different well widths (L = 5 and 25 nm). Several interband transitions have been observed between heavy-hole and light-hole subbands, and conduction subbands at room temperature and at 5 K. Least-squares fits to an Aspnes third derivative functional form yield the energy, broadening parameter, amplitude and phase of the optical transitions. The evolution of the energetic position versus the temperature is fitted using the Varshni semiempirical relationship. A significative modification of the main optical transition E1H1 is evidenced: as the temperature is decreased below 50 K, E1H1 changes from a free to a bound excitonic transition. The energetic positions of four optical transitions in the strained 25 nm quantum well have been compared with the theoretical values obtained by an envelope function model and yield the conduction band offset parameter Qc in the strained InGaAs/InAlAs system with a high accuracy (Qc = 0.73±0.02).

Photo-induced current transient spectroscopy of Al0.48In0.52As semi-insulating layers grown on InP by molecular beam epitaxy

Deep levels in undoped semi-insulating In 0.52 Al 0.48 As layers grown by molecular beam epitaxy on iron-doped InP have been studied by photoluminescence and photo-induced current transient spectroscopy. The effect of the growth temperature T g in the range from 300 o C to 530 o C has been investigated. The results show that low T g causes the material quality to deteriorate and leads to formation of a higher concentration of deep traps. It is shown that optimized material quality can be obtained For InAlAs layers on InP substrates with T g around 530 o C with sufficiently high resistivity, reduced trap density and good structural properties which is appropriate for fabrication of high electron mobility transistors

Room temperature photoreflectance as a powerful tool to characterize the crystalline quality of InAlAs layers grown on InP substrates

Abstract The aim of this work is to show that room temperature photoreflectance can give the same indications as low temperature photoluminescence about the crystalline quality of both layers and interfaces. Our samples consist of molecular beam epitaxy InAlAs layers lattice-matched to InP substrates, grown at different growth temperatures and using different InP cleaning temperatures. The photoreflectance broadening parameter (γ) has been determined and compared with the well-known linewidth broadening of the photoluminescence. Both methods indicate that the best InAlAs crystalline quality is obtained for a growth temperature of 530 ° and an InP surface cleaning temperature of 530 °.

Epitaxial growth and photoluminescence investigations of InP/InAs quantum well grown by hydride vapor phase epitaxy

InAs/InP quantum well (QW) structures are grown on InP substrates by hydride vapor phase epitaxy (HYPE) in a continuous mCi H2 HC1 flow with alternate supply of AsH3 and PH3. Photoluminescence peaks due to InAs QW are clearly detected with the higher energy ever reported (1. 23 eV) and with very good value for the full half width maximum (FHWM up to 1 3 meV). The evolution of the peak emission as a function of thickness leads us to determine a critical thickness of 7-8 ML for the InAs/InP system.

Optical studies of lattice-matched and strained GaInAs/AlInAs single quantum wells

Photoconductivity (PC), photoluminescence (PL), and photoreflectance (PR) have been carried out on In0.52Al0.48As/InxGa1-xAs single quantum wells, in lattice matched and lattice mismatched composition. The unstrained (xIn equals 0.53) and the strained (xIn equals 0.60) samples have been grown by molecular beam epitaxy (MBE), with well thicknesses of 5 nm and 25 nm. Low temperature PL measurements have shown a narrow full width at half maximum (FWHM) for the unstrained samples, indicating a very good interface quality. In strained samples a broadening on the FWHM has been found, indicating a small degradation of the structure quality with the introduction of strain. With the PC and PR measurements we have been able to observe transitions between electron and heavy holes levels (EiHi) up to i equals 5 and also between the first electron and light holes levels (E1L1). We have then calculated the theoretical values of these transitions by solving the Schroedinger equation in a finite square well, using an envelope function approximation, an effective mass approximation, and including the effects of strain on the band structure and on the effective mass. For the lattice matched composition, the best fit is obtained for conduction band offset (Delta) Ec equals 0.50 +/- 0.05 eV, in agreement with the literature. For example, with xIn equals 0.60 composition the best fit is obtained for (Delta) Ec equals 0.55 +/- 0.05 eV, in agreement with theory which predicts that (Delta) Ec increases with indium content.

Characterization of main electron scattering mechanisms in InGaAs/InAlAs single quantum wells by optical modulation spectroscopy

In this paper we report experimental results on InGaAs/InAlAs single quantum wells (SQW) obtained by photoreflectance (PR) between 5 K and 450 K. In the first part of the paper we focus on the evolution of the broadening parameter of E1H1 in the lattice matched 5 nm well width sample, E1H1 and E2H2 in the lattice matched 25 nm SQW. From this study we derive information about the relative influence of interface roughness, alloy scattering, and electron phonon interactions. In the second part we apply the PR technique to the study of quantum wells near the surface in which we observe an increase of the broadening parameter. These studies show the great interest of PR technique for the qualification of materials and for the surface probe.

Materials problems for the development of InGaAs/InAlAs HEMT technology

The materials problems in the In x Ga 1-x As/In 0.52 Al 0.48 gAs on InP(001) system, which potentially affect the performance reproducibility and stability of high electron mobility transistor (HEMT) devices, have been investigated. It is shown that crystalline imperfections and InAlAs growth roughness strongly affect the InGaAs/InAlAs heterostructures. A correlation between the structural and optical properties of InAlAs was shown. The strained In x Ga 1-x As channel is shown to enhance HEMT transport properties for x=0.60 and channel thickness less than 25 nm

Optical characterizations of lattice matched and strained GaInAs/AlInAs single quantum wells

The authors report a study of optical properties of lattice matched (x=0.53) and strained (x=0.60) In/sub x/Ga/sub 1-x/As/In/sub 0.5/Al/sub 0.48/As single quantum wells, grown by molecular beam epitaxy (MBE). A set of optical spectroscopy techniques, namely, photoluminescence (PL), photoconductivity (PC), photoreflectance (PR), and photoluminescence excitation (PLE), have been used. By means of low-temperature PC measurements, the role of strain in introducing some defects is analyzed. The conduction band discontinuity at 300 K and 5 K is determined with data of PR and PLE measurements as a function of x. Results have shown the increase of Delta E/sub c/ values with the increase of indium concentration in the InGaAs quantum well.<<ETX>>